In general, the processing of substrates refers to the various steps performed or carried out to modify either the surface of a substrate material layer, the material layer of substrate itself, or both the surface of the material layer of the substrate and the material layer of the substrate itself in order to modify and change the functionality of the substrate for a specific purpose. The change in functionality of the substrate is often the result of a modification or change in either the actual properties of the material layer of the substrate itself or a change in the actual properties of surface of the material layer of the substrate. The steps performed during substrate processing may be straightforward. For example, a substrate may be heated to either relieve stress by thermal relaxation or to change the physical hardness of the substrate. In both cases changes in the physical properties of the entire substrate material layer and surface take place. In another example of substrate processing, the surface of the substrate material layer may be cleaned using any means known in the art, such as, for example exposure of the substrate material layer to a combination of ultraviolet light and ozone gas, in order to achieve a demonstrable change in an easily measured metric like contact angle when wetted by a drop of a fluid of known surface tension. The processing of the substrate material layer by means of exposure to ultraviolet light and ozone gas is employed to modify the wetting properties of the surface substrate thereby affecting a change in the surface energy of the surface of the substrate material layer. Processing of substrates may be more complicated, involving steps associated with changing the functionality of the material layer substantially by modifying the chemical composition of the surface of the substrate material layer or the material layer of the substrate itself. In particular, the processing of substrates may result in changes in functionality of the substrate or substrate surface that include alteration of the physical properties of the near surface region of the substrate to achieve desirable physical properties such as increased conductivity or increased resistivity, specific optical properties, specific surface energy, specific chemical reactivity, improved surface topography, and the like. Substrate processing to modify the surface of a substrate is well known in the art of fabrication of integrated circuits where the processing steps and sequences of processing steps have specific purposes. For example, deposition processing, often referred to just as “deposition”, may be used to alter the surface composition of a substrate by adding a material layer to a substrate surface by means of a wide variety of methods known in the art for adding a material layer to a surface. Methods for adding a material layer to a substrate or support are well known to those familiar with the art of deposition, can be highly specialized, encompassing a vast array of technologies, and can include such methods as, for example, physical vapor deposition by evaporation and sputtering, chemical vapor deposition, plasma enhanced chemical vapor deposition, electrostatic mist deposition, electrochemical deposition (plating), electroless deposition, spin coating, hopper coating, gravure coating, flexographic printing, silk screen printing, deposition by brush application or spray, electro-spray, thermal plasma, and the like.
Deposition processing is known as an additive processing method because a material layer is added to the surface of the substrate material layer or substrate surface, resulting in a film of measureable thickness placed over and in contact with the substrate surface. Similarly, there is subtractive processing accomplished by means of subtractive processes, that is used to change the functionality of substrate surface by removing a measureable quantity of a material from the substrate surface. Examples of subtractive processes familiar to those knowledgeable in the art of subtractive processing include plasma etching and plasma stripping processes and chemistries, non-plasma based etching and stripping processes employing both the condensed and vapor phase etchant and/or stripping chemistries, electrochemical stripping processes, abrasive polishing processes, cleaning processes, sand blasting, grit blasting, and the like.
The terminology employed in the art for the material layer that is subjected to processes or undergoes processing is highly varied. In this document the material layer that is exposed to and removed from various processing steps and processes is called the substrate. Elsewhere in the art the material layer that undergoes processing is called the support, the workpiece, a slice, a wafer, an object, a web, and is also identified by numerous other terms. The context and description found in the art where the term describing the material layer undergoing processing occurs makes clear when the term “substrate” as employed here can be used interchangeably with the term employed in the art that is used to describe the material layer that is subjected to processes or undergoes processing.
Fluidic Levitation
The substrate processing quality is determined at least in part by the defect levels on the substrate after processing. There are many factors that can prevent acceptable substrate processing by introducing substrate defects. Two factors contributing to substrate defect levels after processing are particle contamination and substrate physical contact. Both particle contamination of the substrate surface and physical contact with either the substrate material layer or the substrate surface can lead to unacceptable substrate defects, some of which are manifest as defects in the uniformity of the surface properties of the substrate after processing. The measurement of the number of defects by any known method such as, for example, light scattering from the surface of the substrate, is known as defectivity. In substrate processing applications where it is important to control defectivity, effort has been made to develop methods that minimize particle contamination and physical contact with the substrate surface. Examples of processes where it is important to control defectivity are optical film deposition, deposition of encapsulation films, and integrated circuit manufacture. In these examples, the substrate may be planar and plate-like, non-planar with complex surface features, spherical, or spheroidal. An example of a planar or plate-like substrate would be a silicon wafer or a glass plate upon which integrated circuit elements are fabricated. An example of a non-planar substrate with a complex shape would be a lens upon which an antireflection film is deposited. A substrate may also be flexible, for example, like a web of polymer film, a flexible web of glass, a long ribbon of metal, or a large sheet of glass. An example of a substrate that is flexible and non-planar is a spool of wire that is to be cleaned prior to application of an electrically insulating coating using additive processing. The desire to minimize particle contamination of the substrate surface and eliminate physical contact with the sample during processing has led to the development of specialized substrate handling methods based on fluidic levitation.
In general, flows of gases over a surface are known and in particular Bernoulli effects are known. Levitation refers to the process of suspending an object in a medium without the use of physical supports contacting the object. In the scientific literature, levitation is the process by which an object is suspended by a physical force, against the force of gravity, in a stable position without the use of physical contact. Fluidic levitation refers to the process of levitation where the physical force suspending the object in a stable position against the force of gravity is produced by means of a fluid said fluid being a moving fluid or a stationary fluid. Fluidic levitation can employ different types of fluids, said fluid being either gaseous compressible fluids or condensed non-compressible liquids. The term compressible refers to a fluid whose density is strongly pressure dependent.
For the purposes of the invention the term “moveable substrate” refers to a substrate that undergoes positional displacement during fluidic levitation upon exposure to a fluidic flow employed for the purpose of inducing fluidic levitation of the substrate and opposing the force of gravity during said levitation state. The term “stationary support” refers to a stationary fluid emitting element that is employed for the purpose of supplying a fluidic flow, said fluidic flow being employed for the purpose of inducing fluidic levitation of the moveable substrate and producing fluidic forces opposing the force of gravity when the moveable substrate is in a levitated state. The term “support during levitation” means that the moveable substrate can be levitated by fluid flow emanating from the stationary support so that gravitational force on the moveable substrate is opposed by the force of a fluidic flow. In contrast to moveable substrates, conventional substrates are fixed in position during processing, for example, using mechanical restraints, vacuum chucks, or electrostatic chucks.
Fluidic levitation is useful for manipulating a substrate during processing and, as a method for sample manipulation, may encompass and advantageously enable many different varieties of substrate processing. There are many substrate processes that require exposure of the substrate surface to chemically reactive substances for the purpose of modifying or changing the properties of the substrate. The prior art disclosing substrate processing with fluidic levitation methods makes little mention of any issues associated with incorporating chemically reactive materials into the levitating fluid flow for the purpose of substrate processing. This is surprising because the problems associated with the handling, manipulation, and fluid transport of chemically reactive materials is well known. Some of these problems are 1) corrosion and dissolution of the materials of construction employed for the pumps, gauges, valves, tubing, and connections in the fluid delivery system leading to equipment failure and 2) deposit build-up at various locations in the fluid system from unintended side reactions of reactive species in the fluid with the materials of construction of the fluid delivery system which can lead to changes in the fluid flow and fluid pressure during fluid delivery system operation. Furthermore, the physical positions of substrates that are subject to fluidic levitation tend to be unstable and the substrate position is mechanically controlled. This mechanical control can induce particulate contamination or damage to the substrate.
U.S. Pat. No. 3,627,590 describes a method for processing a workpiece, for example, a slice of semiconductor material or a wafer of a semiconductor, by floating the substrate on a layer of gas during the series of processing steps required for thin-film processing. Two processes are disclosed in U.S. Pat. No. 3,627,590: heat treatment for enhanced diffusion of a dopant into a film and film deposition by means of thermal decomposition of a thermally unstable precursor. The layer of gas prevents physical contact with the workpiece during processing. The workpiece described in U.S. Pat. No. 3,627,590 is a substrate. U.S. Pat. No. 3,627,590 teaches that film deposition with thermally unstable precursors can be managed when the decomposition temperature of the precursor is high and the thermally decomposable precursor can be kept away from and isolated from portions of the equipment that operate at elevated temperature. However, U.S. Pat. No. 3,627,590 does not teach or disclose a method or apparatus to control and manage the reactivity of the fluid flow as it comes in contact with different surfaces of the fluid delivery system and associated equipment.
The apparatus described in U.S. Pat. No. 3,627,590 is called a pressurized fluid pickup device and is described further by Mammel in U.S. Pat. No. 3,466,079. In U.S. Pat. No. 3,466,079 the term “slice” is used to describe the substrate. According to U.S. Pat. No. 3,466,079 it is “ . . . nearly impossible to center the exit orifice for the pressurized fluid over the support . . . . As a result, there is a force component tending to laterally shift the slice relative to the reference surface”. This is another way of saying that, left to itself, the slice—which is the substrate—will shift and move laterally in a sidewise manner until none of the surface area of the slice is exposed to the pressurized fluid flow. Lateral motion means that the substrate moves horizontally in a sidewise manner that is parallel to the stationary support and the plane of the layer of gas upon which the substrate is floating. In other words, the lateral motion of the substrate slice moves the substrate away from the pressurized fluid emitting from the reference surface resulting in a failure of the sample to float on the gas layer. The problem identified by Mammel in U.S. Pat. No. 3,466,079 is one of uncontrollable lateral motion of the substrate during fluidic levitation because of the difficulty associated with positioning the substrate in the proper position over the pressurized fluid region. This problem is addressed in U.S. Pat. No. 3,466,079 by the use of physical contact with the substrate: “Shifting of the slice is limited by the lugs 25 with either the points 26 or the rounded ends 26”. In both U.S. Pat. Nos. 3,627,590 and 3,466,079 the substrate is kept in place over the pressurized fluid flow by the use of stops or lugs to prevent the sample from shifting position during processing.
The scientific literature describes a method for substrate handling during processing known as “vapor levitation” in which the substrate floats on a cushion of gas emanating from a porous surface opposed to one of the substrate surfaces. This method of substrate handling differs from that described in U.S. Pat. No. 3,627,590 but possesses a commonality in the difficulty of maintaining the sample position during processing due to the frictionless nature of the gaseous floatation layer which enables non-contact processing. The method is described by H. M. Cox, S. G. Hummel and V. G. Keramidas in the following publications: 1) “Vapor Levitation Epitaxial Growth of InGaAsP Alloys Using Trichloride Sources” Inst. Phys. Conf. Ser. No. 79: Chapter 13, page 735 (1986); 2) “Vapor Levitation Epitaxy: System Design and Performance”, J. Crystal Growth 79(1986) 900-908; 3) “Vapor Levitation Epitaxy Reactor Hydrodynamics” by J. S. Osinski, S. G. Hummel and H. M. Cox, Journal of Electronic Materials 16(6) (1987) 397-403. The fluid delivery system employed for vapor levitation epitaxy is described in detail by Cox, Hummel, and Keramidas in the article “Vapor Levitation Epitaxy: System Design and Performance” (J. Crystal Growth 79(1986) 900-908). Deposition processes that can occur in the fluid-delivery system are managed by operating the entire fluid-delivery system at elevated temperature and continually scrubbing by contacting the surfaces of the fluid delivery system with reactive gases to clean the surfaces of the fluid delivery system. The fluid-delivery system employed for fluidic levitation of a substrate and substrate processing disclosed in this art does not teach or disclose a method or apparatus to control and manage the reactivity of the fluid flow as it comes in contact with different surfaces of the fluid delivery system and associated equipment.
U.S. Publication No. 20080122151A1 by Ito, Niwa, and Saito titled “Levitation Unit with Tilting Function and a Levitation Device” describes a device comprised of a frictionless spherical joint enabling frictionless tilting of a porous gas emitting surface which is employed for vapor levitation to support large planar objects. The mechanical instability of the device described in U.S>Publication No. 20080122151A1 makes it difficult to see how the device can achieve fluidic levitation of a substrate body on the porous gas emanating surface and keep the substrate body in a stable position with little or no lateral movement.
U.S. Pat. No. 6,805,749B2 by Granneman et al. titled “Method and Apparatus for Supporting a Semiconductor Wafer During Processing” describes a method for contactless processing or treatment of a substrate such as a semiconductor wafer comprising enclosing the wafer in an apparatus and applying two gas streams in opposing directions from first and second side sections located opposite one another to the two opposing planar sides or surfaces of the wafers. Although the use of multiple gas streams or jets is mentioned as a means of providing the levitating fluidic flow, the preferred method of production of the gas streams is through the use of porous plates wherein the porous plates provide the gas passages to produce the gas streams that are used for vapor levitation according to the method described by Osinski, Hummel and Cox in Journal of Electronic Materials 16(6) (1987) 397-403. There is no teaching regarding elimination of lateral movement of the substrate in U.S. Pat. No. 6,805,749B2 and the method described suffers the same shortcomings common to all vapor levitation technology. U.S. Pat. No. 6,805,749B2 mentions that the problem of “supplying process gas at elevated temperature and more particularly when depositing layers is that the apparatus used to supply the process gas becomes contaminated by deposition of the material concerned from the process gas. This means that apparatuses of this type have to be cleaned regularly and that major problems arise with regard to clogging.” [Col 3, lines 9-17] This problem is managed in U.S. Pat. No. 6,805,749B2 by operating the apparatus in a temperature region where minimal deposition can occur whilst not eliminating the problem. The fluid delivery system employed for fluidic levitation of a substrate and substrate processing disclosed in this art discloses the use of temperature control as a method to control and manage the reactivity of the fluid flow as it comes in contact with different surfaces of the fluid delivery system and associated equipment.
U.S. Pat. No. 6,805,749 B2 further teaches the use of the “Bernoulli principal” for substrate handling suggesting that the “the Bernoulli principle can be used by allowing the correct gas stream to flow against the top of the wafer. With this arrangement a reduced pressure is created beneath the wafer which reduced pressure ensures that the wafer will float (in a stable manner) beneath the top side section.” U.S. Pat. No. 6,805,749 B2, contrary to all other prior art including the art of U.S. Pat. No. 3,466,079, claims that the substrate will “float (in a stable manner) beneath the top side section” in this arrangement. U.S. Pat. No. 6,805,749 B2 does not describe “the correct gas stream” and the specification of the document is insufficient to determine exactly what apparatus was employed to achieve the reported result. It is thoroughly clear that U.S. Pat. No. 6,805,749 B2 does not contain a description of any addition modification of the apparatus or disclose a specialized method that would enable vapor levitation with the sort of positional stability therein described, and thus teaches against the art disclosed by Mammel in U.S. Pat. No. 3,466,079 and others. U.S. Pat. No. 6,805,749 B2 also describes a method of achieving substrate rotation by altering gas emanating channels 10. Substrate rotation can be achieved by “positioning one or more of the channels 10 at an angle with respect to the vertical, as a result of which a spiral gas flow is generated.” No further detail concerning substrate rotation is disclosed and it is unclear exactly how this rotation is implemented in the disclosed apparatus or whether stable rotation can be achieved using the disclosed apparatus.
U.S. Pat. No. 5,155,062 by Thomas G. Coleman entitled “Method for Silicon Carbide Chemical Vapor Deposition Using Levitated Wafer System” describes a method of chemical vapor deposition of silicon carbide on a substrate where the substrate is suspended in an upward flow of gas and heated using either induction heating or microwave heating to address control of the extremely high temperatures required to prepare the desired polytype of SiC on the substrate. The method of fluidic levitation is not well described and appears to be similar to that described in U.S. Pat. No. 3,627,590. No teaching on the preferred method of fluidic levitation is given in U.S. Pat. No. 5,155,062 and there is no detail on how reactive fluids are handled in the apparatus. U.S. Pat. No. 5,155,062 teaches the use of highly localized heating methods such as inductive heating of the substrate or microwave heating of the substrate to ensure that thermal decomposition of the precursor occurs only where elevated temperatures are present. The apparatus and method in this art discloses only the use of temperature control as a method to control and manage the reactivity of the fluid flow as it comes in contact with different surfaces of the fluid delivery system and associated equipment. Although not shown in the drawings, U.S. Pat. No. 5,155,062 explicitly calls out a “means for aligning the substrate . . . in the form of the supporting shoulders 12a” (FIG. 1). In FIG. 2 of U.S. Pat. No. 5,155,062 the suspended substrate that is fluidically levitated is located within a cavity that restrains the lateral movement of the substrate during fluidic levitation. FIGS. 1 and 2 in U.S. Pat. No. 5,155,062 indicate that Coleman recognized the difficulty in maintain the substrate in a suitable position during processing and resorted, as in the previous art, to the use of a physical restraint, in this case a “shoulder” on the substrate support or a cavity around the substrate in order to maintain the substrate in a stable position.
U.S. Pat. No. 5,370,709 by Norio Kobayashi titled “Semiconductor Wafer Processing Apparatus Having a Bernoulli Chuck” describes a method and apparatus for non-contact processing of a substrate using a pressurized gas flow method similar to that previously disclosed in U.S. Pat. No. 3,627,590. On a central portion of a suction plate in a reaction chamber, there is formed a blowing port for blowing gas to a rear surface of the suction plate. In the blowing port, there are provided pipes for introducing carrier gas and reactant gas. Gas, which is introduced by these pipes, and the suction plate are heated by a lamp formed in the outside of the reaction chamber. If gas introduced by these pipes and reactant gas are blown from the blowing port to the rear of the suction plate in a state that a semiconductor substrate is close to the portion in the vicinity of the suction plate, the semiconductor substrate is sucked to the suction plate in a noncontact state and an epitaxial layer is formed on the semiconductor substrate in this state.
The particular process disclosed in U.S. Pat. No. 5,370,709 involves the film formation on a pneumatically levitated substrate by means of thermal decomposition of a thermally decomposable volatile precursor. The apparatus disclosed uses a single orifice for delivery of the fluid flow containing the thermally decomposable reactive precursor. The thermally unstable gas phase reactant is injected into a preheated carrier gas near the fluid deliver orifice and col. 5, lines 39-41 reads “The reason why reactant gas is mixed with the preheated gas is to prevent the chemical reaction of reactant gas due to heat.” It is apparent that Kobayashi recognized the issues involved in fluid delivery of reactant species during fluidic levitation.
Although the apparatus and method in U.S. Pat. No. 5,370,709 attempts to control the reactivity of the fluid flow by controlling the temperature of the fluid flow it is difficult to see how unintended deposition of the reactive precursor would not occur in the orifice itself during the semiconductor wafer processing operation since the orifice region is heated, also. With continued deposition in the heated vapor delivery orifice during equipment operation, the orifice will eventually block, resulting in equipment failure as the diameter of the orifice decreases with increasing deposition. Thus, U.S. Pat. No. 5,370,709 teaches the use of temperature control as a method to control and manage the reactivity of the fluid flow as it comes in contact with different surfaces of the fluid delivery system and associated equipment during fluidic levitation.
The initial “parallel plate” configuration disclosed in FIG. 1 of U.S. Pat. No. 5,370,709 has no physical restraints for lateral movement of the substrate during levitation and by virtue of its similarity with the apparatus described in U.S. Pat. No. 3,466,079 would suffer from the same problem of positional stability and lateral movement of the substrate during operation thereby resulting in a useless apparatus. All subsequent configurations disclosed in U.S. Pat. No. 5,370,709 employ the use of “stoppers” around the periphery of the substrate while it is floating on the fluid layer of gas to prevent lateral motion of the substrate and keep the substrate from sliding out of position on the nearly frictionless gaseous support layer. For example the description of FIG. 2 of U.S. Pat. No. 5,370,709 reads “The rear surface portion of the suction plate 26 is formed to be smooth and a stopper 31 is provided at four places in the periphery of the rear surface portion.” Only two of these stoppers 31 are shown. The suction plate 26, the stopper 31, the pipes, 27, 28, 30 and the nozzle 29, are made of quartz respectively. Thus, U.S. Pat. No. 5,370,709 teaches the necessity of physical stops formed on the suction plate 26 to prevent lateral motion of the substrate during fluidic levitation.
The pneumatic levitation of spherical objects in a gaseous fluid flows is known. U.S. Pat. No. 4,302,311 entitled “Sputter Coating of Microspherical Substrates by Levitation” discloses pneumatic levitation of microspheres under reduced pressure conditions. The moveable substrate is a glass bead microsphere of varying weight and size and the gas-emanating stationary support has a complex structure. The stationary support provides a gas emanating from a collimated-hole structure held in place by an alignment spacer. The disclosure describes the use of shaped collimated hole structures to achieve pneumatic levitation of non-porous glass microbeads under low-pressure conditions. The collimated hole structure employed in U.S. Pat. No. 4,302,311 is a stationary porous gas emitting surface that is shaped with a depression that follows the spherical surface topography of the moveable microspherical substrate to be levitated. Gas uniformly flows underneath the spherical substrate during pneumatic levitation. In this case the ambient environment in which pneumatic levitation is performed is unusual and the ambient pressure during pneumatic levitation is below 500 mTorr—in other words, the pneumatic levitation was performed under reduced pressure conditions. The collimated-hole structure provides multiple parallel gas jets that are used for pneumatic levitation of the microspherical substrates and the gas-emanating collimated-hole structure is “dimpled”—meaning that is has depressions in which the glass microspheres sit. The “dimpled” structure can be hemispherical, cylindrical, or conical. The height of the microspherical substrate above the bottom of the dimple is monitored during pneumatic levitation. The parallel gas jets from the collimated hole structure as well as physical barriers around the gas emitting depressions help keep the microspherical substrates in a stable position during pneumatic levitation and the reactive fluid comprised of a sputtered flux of metal species employed for depositing metal films on the levitating microspherical substrates is incident normal to the collimated hole structure, directly opposing the fluid flow of the levitating jets from the collimated hole structure. The “dimples” of the gas emanating collimated hole structure—meaning the depressions in which the glass microspheres sit—are actually a means of providing a physical stop to keep the spherical substrate in place during pneumatic levitation. The alignment spacer also provides an additional second physical stop that keeps the microspheres in place during pneumatic levitation. U.S. Pat. No. 4,302,311 is an example of managing the reactivity of a fluid flow in a fluid delivery system by means of opposing fluid flows that prevent contact between a reactive fluid and a critical component of the fluid delivery system used for substrate levitation. It is disclosed in the scientific literature and the levitation art dating prior to that of U.S. Pat. No. 4,302,311 that spherical objects will exhibit stable levitation with rotation in a directional gas flow of sufficient velocity and volumetric flow.
U.S. Pat. No. 4,378,209 by Berge, Oran, and Theiss titled “Gas levitator having fixed levitation node for container-less processing” discloses a method and apparatus for processing spherical objects during pneumatic levitation where the levitation is accomplished by use of an “elongated levitation tube having contoured interior in the form of convergent section 12, constriction 15, and divergent section 14 wherein the levitation node 16 is created”. The elongated levitation tube with levitation node is disclosed to be suitable for containerless processing of pneumatically levitated spheres and right circular cylinders. The walls of the elongated levitation tube in U.S. Pat. No. 4,378,209 provide physical stops and a means of confinement of the sample during establishment of pneumatic levitation in the levitation node of the apparatus. It is known in the open scientific literature and the art of fluidic levitation that solid spherical objects can be stably levitated in a fluidic flow of sufficient velocity and volumetric flow when the spherical object is allowed to freely rotate in the flow.
U.S. Pat. No. 4,378,209 further discloses the use of an additional concentric tube within the elongated levitation tube that can be employed for various purposes such as supplying solid material to the levitated object or supplying an additional fluid flow whose initial flow direction opposes the fluid flow of the main elongated levitation tube. U.S. Pat. No. 4,378,209 is an example of managing the reactivity of a fluid flow from a fluid delivery system by employing opposing fluid flows during fluidic levitation in order to control contact between a reactive fluid and components of the fluid delivery system used for substrate levitation.
U.S. Pat. No. 4,969,676 titled “Air pressure pick-up tool” by LaMagna discloses a modification of the Bernoulli type pick-up tool disclosed by Mammel in U.S. Pat. No. 3,466,079. The improvement disclosed in U.S. Pat. No. 4,969,676 is the inclusion “of a cavity in the major surface of the head member surrounding the air passage . . . ” of the device disclosed in U.S. Pat. No. 3,466,079. The cavity on the bottom surface of the Bernoulli type pick-up is proximate to the exit orifice where gas is injected into the gap between the pick-up surface and the substrate surface and is believed to produce more uniform radial flow of fluid along the substrate surface. U.S. Pat. No. 4,969,676 discloses the use of physical stops to restrain lateral movement of the substrate during fluidic levitation of the planar substrate.
U.S. Pat. No. 5,067,762 titled “Non-contact conveying device” by Akashi discloses a Bernoulli type pick-up tool comprised of a novel gas injection cavity and rim whereupon increased Bernoulli lift force is produced at the levitating substrate surface during fluid flow. U.S. Pat. No. 5,067,762 describes an apparatus comprised of a “cushion-vacuum room” and a Bernoulli surface. U.S. Pat. No. 5,067,762 specifically discloses a “non-contact conveying device that has a guide means to prevent lateral movement of articles.” The guide means disclosed in U.S. Pat. No. 5,067,762 comprises “a plurality of bars extending radially and having stoppers extending below the plane in which the Bernoulli surface 4 exists. Also some bars 10a may have steps 10b to contact certain parts of the surface of the article B where contact is acceptable. Article B is prevented from lateral movement and can be placed at a desired position” (col. 7, lines 39-43). Article B is the substrate. U.S. Pat. No. 5,067,762 thus discloses the use of physical stops to restrict substrate motion of planar substrates during fluidic levitation employing gaseous fluids.
WO 96/29446 entitled “Chemical Vapor Deposition of Levitated Objects” by West and Criss discloses an apparatus and a method for deposition rhenium metal films on spherical carbon moveable substrates that are pneumatically levitated under reduced pressure conditions. The gas emanating stationary support is a funnel shaped and provides physical stops that can prevent the pneumatically levitated spherical moveable substrate from moving out of the levitating gas flow. It is known in the open scientific literature and in the patent art dating prior to WO 96/29446 that a solid spherical object can be stably levitated in a fluidic flow when the spherical object is allowed to rotate in a gas flow of sufficient volumetric flow and velocity.
U.S. Pat. No. 5,096,017 by Rey and Merkeley titled “Aero-acoustic levitation device and method” discloses the levitation of the specimen object using a concentrated flow of gas and stabilizing the position of the specimen object using acoustic positioning forces generated by acoustic waves during heating and cooling of the specimen object. The specimen object is spatially confined at the nodes generated by the interacting acoustic positioning forces thus producing stable levitation of the specimen object and achieving container-less processing of the specimen object during heating and cooling of the specimen object. Although it is known in the art that solid spherical objects can be stably levitated in a fluidic flow when the spherical object is allowed to rotate in a fluid flow of sufficient volumetric flow and velocity, U.S. Pat. No. 5,096,017 discloses an apparatus and method by which non-rigid spherical objects, such as liquid or molten liquid drops, can be stably levitated.
U.S. Pat. No. 5,492,566 by Sumnitsch titled “Support for disk-shaped articles using the Bernoulli principle” discloses an apparatus for supporting disk shaped articles. The surface of the apparatus is circularly shaped and equipped with an annular gas ejection nozzle that provides gas flow of sufficient velocity to pneumatically levitate a substrate facing the support surface. The lateral motion of the substrate during pneumatic levitation is prevented by the introduction of at least one mechanically fixed elastic support pad or at least one mechanically fixed elastic support structure located on the surface of the apparatus that contact the opposing substrate surface when the substrate is pulled down towards the apparatus surface by the Bernoulli effect when gas is ejected from the annular nozzle. U.S. Pat. No. 5,492,566 does not disclose a non-contact method for stabilizing the position during pneumatic levitation. The substrate contacts an elastic pad during pneumatic levitation in U.S. Pat. No. 5,492,566.
U.S. Pat. No. 5,967,578 by Frey titled “Tool for the contact-free support of plate like substrates” discloses a tool for handling plate-like circular wafers equipped with a circular “dynamic” gas distribution chamber and an annular gas ejection nozzle that provides gas flow of sufficient velocity to pneumatically levitate a substrate facing the support surface. The lateral motion of the substrate during pneumatic levitation is prevented by the introduction of at least two guiding means arranged at spaced locations to each other and extending vertically with respect to the surface of the tool at a distance besides the gas emitting annular slit.” These guiding means are arranged in such a way as to provide “contact points” or “contact lines” for the outer periphery of the wafer to be treated”. The guiding means are intended to restrain the lateral motion of the substrate during pneumatic levitation when the tool is employed for supporting a circular plate like substrate.
U.S. Pat. No. 7,328,617 B2 titled “Air levitation apparatus with neutralization device and neutralization methods for levitation apparatus” by Miyachi, Nishikawa, and Suzuki discloses an air levitation device employed to transport plate shaped work, such as thin plates of material like glass, wherein the air levitation device comprises a means of air ionization and a levitation apparatus providing a plurality of air jets as a means of levitating the plate shaped work. The means of air ionization is a corona discharge device employing at least one needle-shaped electrode. The air levitation apparatus of U.S. Pat. No. 7,328,617 B2 is intended as a means of substrate transport, both allowing motion of the plate and providing a means of motion to the plate shaped work and thus the apparatus does not have a function of providing air levitation or pneumatic levitation wherein the plate shaped work is motionless or laterally restricted in motion.
U.S. Publication No. 2007/0215437 A1 titled “Gas bearing substrate-loading mechanism process” by Cassagne discloses pneumatic levitation of a thin plate-like substrate by means of flotation on a layer of gas produced by a plurality of gas emitting ports. Adjacent to these ports and spatially intermingled with the gas emitting ports are vacuum port employed to keep the thin plate-like substrate stationary when required. U.S. Publication No. 2007/0215437 A1 teaches the use of robotic grippers—also called a “clamping system”- or a “pushing/pulling” system to restrict and control the normally unimpeded motion of the substrate on the frictionless gas layer. U.S. Publication No. 2007/0215437 A1 teaches that a system of mechanical restraints is necessary when employing fluidic levitation to levitate a substrate while restricting undesired lateral motion of the substrate.
U.S. Publication No. 2012/0110528 A1 titled “Device and method for the contactless seizing of glass sheets” by Herfert discloses an apparatus for moving large glass sheet with no physical contact to the glass sheet where the gripping force is supplied by balancing a suction force supplied by reduced pressure in a cup with a positive pressure supplied by atmospheric pressure ultrasonic waves. No physical restraints to restrict the movement of the levitated glass sheet are disclosed. The apparatus of U.S. Publication No. 2012/0110528 A1 effectively levitates the large glass sheet at several different locations on the glass sheet substrate and as a result levitates the entire sheet. In the absence of constant adjustment of the levitation position or the use of physical restraints on the perimeter of the substrate, the glass sheet will not remain stationary due to the frictionless nature of the levitation method employed and the glass sheet will begin to be transported in a manner similar to U.S. Pat. No. 7,328,617 B2.
U.S. Pat. No. 6,601,888 B2 titled “Contactless Handling of Objects” by McIlwraith and Christie discloses a method and apparatus for handling large lithographic plates. The disclosed apparatus is a vibration dampening Bernoulli type pick-up device, similar in concept to that disclosed by Mammel in U.S. Pat. No. 3,466,079. U.S. Pat. No. 6,601,888 B2 teaches that flexible plate-like objects will vibrate and emit high intensity acoustic signals when levitated using a Bernoulli type pick-up device and the intensity of the acoustic signals produced during pneumatic levitation can be reduced by introducing a vibration-attenuating surface into the Bernoulli type pick-up device over which the fluid must flow during the levitation process. The vibration—attenuating surface can be prepared by numerous methods, including modifying the surface near the fluid exiting edges of the Bernoulli type pick-up device with ridges, fibers, bristles, or other physical features that can cause interruption of the fluid flow as the pressure of the fluid equalized with the surrounding medium. U.S. Pat. No. 6,601,888 B2 acknowledges that “preventing lateral movement of objects” that are levitated is a problem but does not provide any teaching or inventive disclosure concerning how to address this problem other than to mention the previously disclosed teaching in the art of fluidic levitation concerning the use of physical stops and barriers to prevent substrate motion.
U.S. Pat. No. 8,057,602 B2 by Koelmel et al titled “Apparatus and Method for Supporting, Positioning and Rotating a Substrate in a Processing Chamber” discloses a method and apparatus employing fluids injected through ports on a baseplate support, said fluid contacting a surface of a substrate to control substrate position and rotation. At least 3 ports adapted to receive a fluid from a flow controller and direct the fluid in different directions are employed and at least a portion of the flow of the fluids from the plurality of ports are adapted to support the weight of the substrate. The fluid flow can be either sub-sonic or super-sonic and the advantages of different fluid flow velocities are contemplated for the purposes of providing momentum transfer to a substrate supported by a fluid layer of any type, gaseous or condensed, in order to bring the substrate into a desired position. A process control loop for fluid flow to each port based on sensor feedback indicating the substrate position is contemplated and the process control loop is used to adjust the fluid flow to each port in the plurality of ports in order to stabilize and control the substrate position. Both software and hardware implementations of the control loop are contemplated. The ports contemplated in U.S. Pat. No. 8,057,602 B2 may be employed to add or remove fluid from the volume between the substrate and the substrate support base plate. The use of thermal edge barriers to restrict overall substrate motion and improve process temperature uniformity is discussed and taught as part of the apparatus. The apparatus described appears complex, requiring control of fluid through multiple fluid ports with complicated electrical feedback circuits being required. The contemplated invention of U.S. Pat. No. 8,057,602 B2 still invokes the use of physical stops called “thermal edge barriers” as an integral part of the apparatus in order to restrict the unpredictable motion of the substrate motion that can occur while the substrate is supported by the essentially frictionless layer of fluid, although the invention claims to solve the problem of physical contact between the substrate and any proximate apparatus employed to provide a means of additional processing during substrate handling by the levitation apparatus.
The scientific literature further discloses additional methods for achieving fluidic levitation with gaseous fluids. Dini, Fantoni, and Failli (G. Dini, G. Fantoni, and F. Failli; “Grasping leather plies by Bernoulli grippers”, CRIP Annals, Manufacturing Technology 58 (2009) 21-24) disclose the use of several variants of Bernoulli type pick-up tools for use with leather plies. Li, Kawashima, and Kagawa (X. Li, K. Kawashima, and T. Kagawa; “Analysis of vortex levitation”; Experimental Thermal and Fluid Science, 32 (2008) 1448-1454) disclosed a novel apparatus and method for fluidic levitation which they call “vortex levitation”. The apparatus for producing vortex levitation is similar to that disclosed by Akashi in U.S. Pat. No. 5,067,762. As with Akashi, gas is injected into a gas injection cavity—which appears identical to the “cushion-vacuum room” described by Akashi. The gas injection cavity is essentially cup shaped and the gas is injected in the cup at a specific location: the vortex levitation cup of Li et al employs a fluid under pressure that is injected tangentially to the walls of the cup shaped gas injection cavity to induce a swirling flow that exits the gas injection cavity through a rim that functions as a Bernoulli surface. Li et al disclose the use of “a set of vortex cups to achieve better stability and a larger lifting force” on what appears to be a plate shaped object but no further details are provided. Wu, Ye, and Meng (Particle image velocimetry studies on the swirling flow structure in the vortex gripper”, Proceedings of the Institution of Mechanical Engineers, Part C, Journal of Mechanical Engineering Science 0(0), (2012)1-11; DOI:10.1177/0954406212469323) report a characterization of the fluid movement in a modified vortex gripper during vortex levitation. The modified design investigated by Wu et al introduced a conical frustum in the center of the cup shaped gas injection cavity of the vortex levitation apparatus described by Li et al which was used to simplify particle imaging during levitation.
The scientific article “Levitation in Physics” by E. H. Brandt (Science vol. 243, pg 349-355, 1989) outlines the physical effects allowing for free floatation of solids and even liquid matter. Among the levitation methods disclosed are levitation methods employing a variety of means including jets of gas, sound waves, beams of laser light, radio-frequency fields, charged particles in alternating electric fields, magnetic repulsion, flux pinning of superconductors and the like. Brandt states that “the main problem in the physics of levitation is stability: the levitated body should not slip sideways but should be subjected to restoring forces in all directions horizontally and vertically when it is slightly displaced from its equilibrium position.” Brandt discusses the stable levitation of spheres is a flowing jet of gas in the section on “Aerodynamic Levitation”, commenting that there are certain apparatus configurations for aerodynamic levitation of spherical objects which are essentially independent of orientation and gravity. There is no discussion of aerodynamic levitation, also known as pneumatic levitation, of disc-shaped objects, plate shaped objects and articles, or other types of planar objects such as planar rectangular shapes, or non spherical object suggesting that, at the time of publication, there is no known method for achieving stable pneumatic levitation of such an object and preventing the sideways slip and lateral motion of the object during the levitation process without physical contact to the sample or the introduction of some sort of additional external restoring force that is imposed upon the intrinsic fluidic forces introduced by the levitation process itself.
Theoretical fluid mechanic analysis of pneumatic levitation processes concludes that it is impossible to fluidically levitate a disc (workpiece) with a single jet of a gaseous fluid except in one specific configuration. A. D. Fitt, G. Kozyreff, and J. R. Ockendon in a paper titled “Inertial Levitation” write in the Journal of Fluid Mechanics (J. Fluid Mech. (2004) vol 508, pp 165-174; page 172 concluding remarks) with respect to moveable substrate levitation with an orthogonal gaseous fluid jet the following: “Of course, if air were blown through a single hole of sufficient radius in the base plate, levitation could not occur because of the pressure drop as the air accelerates in the layer. In fact, it is possible to support a plate by this method by placing the base plate above the workpiece. It can also be supported in such an upside-down configuration by suction through the base plate, and this technique is also used in the glass industry.” Fitt et al. indicate that pneumatic levitation of planar workpiece or planar moveable substrate when the fluid emitting baseplate is below the workpiece will not occur. The remarks by Fitt et al. in a peer reviewed scientific journal indicate that a method or apparatus to fluidically levitate a substrate in a stable manner with a fluid flow emanating from a support beneath the substrate is apparently not known and not obvious to those skilled in the art of fluid mechanics.
Pressurized fluid flow devices for the purpose of substrate levitation or flotation on a gaseous layer or gaseous cushion have been integrated into other technologies specifically for the purpose of preventing physical contact with a surface of said substrate during transport or alignment. U.S. Pat. No. 5,470,420 describes the use of pressurized fluid flow devices as a means of handling adhesive labels and preventing contact with the surfaces of the label. A pressurized fluid flow device is employed to support wafer substrates for transport and pre-alignment prior to electrostatic chucking or placement of the substrate on automated inspection systems. In these examples, physical stops such as edges, pins, or walls are employed in the apparatus to provide a barrier to lateral movement of the substrate wafer and to stabilize the substrate position during substrate transport and subsequent alignment operations so that sideways motion of the substrate is prevented while the substrate is suspended on the frictionless gaseous layer or cushion located between the substrate and the proximate fluid emitting support containing one or more nozzles, gas injection cavities, or orifices that provide pressurized fluid between the substrate and the fluid emitting support containing at least one fluid emitting nozzle or fluid emitting orifice employed as a means to provide Bernoulli lift.
Levitation processes can be carried out with both compressible and non-compressible or incompressible fluids. Levitation processes with compressible fluids are also referred to as pneumatic levitation processes or just pneumatic levitation and are commonly achieved through the use of gaseous fluids. Common gaseous fluids employed for pneumatic levitation are air, nitrogen, other inert gases such as argon, and other gases that remain in the gas phase under the conditions encountered by the gas during pneumatic levitation. Levitation processes with non-compressible or incompressible fluids are also referred to as hydraulic levitation processes or just hydraulic levitation and are commonly achieved through the use of incompressible fluids such as liquid phase fluids such as water, various types of specially formulated oils, or other liquid fluids that remain in the liquid phase under the conditions encountered by the liquid during hydraulic levitation.
Stabilizing Lateral Substrate Movement
Most of the previous efforts directed towards stabilizing the position of a non-spherical substrate, including plate-like substrates, during levitation and preventing lateral movement of the substrate during levitation have focused on the use of physical restraints such as walls and stops to constrain and prevent the lateral motion of the substrate during levitation. Other efforts to stabilize substrate position and control lateral motion during levitation have employed complicated schemes for using supplemental fluid flows whose direction must be somehow controlled to introduce appropriate directional corrective forces on the substrate by transfer of momentum from the fluid used as the medium for levitation. This complicated process of fluid momentum transfer to control lateral substrate motion must occur during and in the presence of the gaseous fluid flow employed as a means of achieving fluidic pneumatic levitation and Bernoulli lift. Such schemes are difficult to implement, can lead to levitation height instability and positional oscillation as a result of unstable fluid flows, and require complicated pneumatic control sequences and feedback control loops for execution.
Examples of non-orthogonal jets and their uses are described by Yokajty in U.S. Pat. No. 5,470,420 where tilted jets are employed specifically to transfer momentum from the gaseous fluid flow of the jets so as to induce lateral movement of the substrate movement during pneumatically levitation of the substrate. U.S. Pat. No. 5,470,420 by Yokatjy discloses the use of arrays of tilted jets, (jets which are non-orthogonal with reference to the stationary support surface normal), for the purpose of intentionally destabilizing the position of a movable substrate and inducing substrate movement in a predetermined direction, either rotationally about an axis or in a specific direction parallel to the stationary support surface. In U.S. Pat. No. 5,470,420 the moveable substrate is a label. According to Yokajty, the gaseous flow from the tilted jet array gives rise to an attractive force between the substrate and the stationary support. In describing the interactions that occur when the label is pneumatically levitated by a tilted jet array, Yokajty states with respect to the action of tilted jet causing pneumatic levitation that “The flow of gas causes a zone of reduced gas pressure to be formed between the support surface 52 and label 14, in accordance with the Bernoulli Effect, thereby establishing a pressure differential across the label to hold the label in position on a film of gas flowing over the support surface.” In U.S. Pat. No. 5,470,420 it is not clear where this pressure differential occurs and, additionally, the specific objective of the invention is to induce movement of the pneumatically levitated substrate so that it can be properly aligned against a set of stops which physically interrupt the substrate movement. In U.S. Pat. No. 5,470,420 tilted jets are employed specifically to transfer momentum from the gaseous fluid flow of the jets so as to induce substrate movement, including rotational movement, during pneumatically levitation of the substrate. The use of tilted jets, either singly or in an array, excludes the possibility of gaseous fluid flow that is symmetrical about the jet; instead, the gaseous fluid flow patterns generated by tilted jets and tilted jet arrays have strong velocity components which are determined by the tilted jet velocity vectors. The flow velocity vectors generated by tilted jets are neither orthogonal nor parallel to the opposing moveable substrate surface. The pneumatic levitation accomplished by means of tilted jets like those described in U.S. Pat. No. 5,470,420 is sometimes referred to as Bernoulli airflow.
Interestingly, the descriptions by Yokajty in U.S. Pat. No. 5,470,420 of the action of orthogonal jets that are found in the description of FIG. 10 state that orthogonal jets are used to “blow the label onto the article to be labeled” (col. 6 lines 4-6) indicating that according to Yokajty, orthogonal jets cannot show attractive forces or pneumatic levitation of substrates. U.S. Pat. No. 5,470,420 does not teach pneumatic levitation of objects with orthogonal fluid jets. U.S. Pat. No. 5,470,420 does not teach pneumatic levitation of a moveable substrate using both tilted jets and orthogonal jets simultaneously.
U.S. Pat. Nos. 5,492,566 and 5,967,578 disclose the use of an annular nozzle comprised of an infinitely large number of tilted jets for the purpose of producing pneumatic levitation by means of Bernoulli airflow and supporting a moveable substrate 12. Annular nozzles of the type described in U.S. Pat. Nos. 5,492,566 and 5,967,578 are formed when the spacing between a plurality of tilted jets positioned around the circumference of a circle becomes infinitely small and the plurality of orifices from whence the tilted jets emanate are arranged about the circumference of a circle in such a manner that projection of each tilted jet on the gas emanating surface is aligned parallel to a radius of said circle and the fluid flow of each tilted jet is directed away from the center of the circle. The annular nozzle structure disclosed in U.S. Pat. Nos. 5,492,566 and 5,967,578 produces a symmetric radial flow field flowing directionally outward and away from the center of the annular nozzle structure and centered around the centroid of the annular nozzle structure. The pneumatic levitation produced by the apparatus in U.S. Pat. Nos. 5,492,566 and 5,967,578 is unstable with respect to lateral movement of the opposing substrate for the reasons cited in U.S. Pat. No. 3,466,079 because it is nearly impossible to center the centroid of the moveable substrate over the centroid of the annular nozzle structure. Both U.S. Pat. Nos. 5,492,566 and 5,967,578 teach the use of physical stops to restrain lateral movement of a substrate pneumatically levitated by means of an annular nozzle structure.
FIG. 1a illustrates one embodiment of the prior art and shows a cross-sectional view of a gas-emanating stationary support 12 containing a single fluid collimating conduit, nozzle, bore, or orifice 14 that is in fluid communication with a pressurized manifold (not shown). Orifice 14 is hereafter referred to as a fluid collimating conduit 14 and fluid collimating conduit 14 can be employed with liquids or gasses. A fluid collimating conduit employed with flowing gas is also called a gas collimating conduit. A fluid collimating conduit employed with flowing liquid is also called a liquid collimating conduit. Dashed normal line 16 is normal to an opposing surface of moveable substrate 10 and to the gas-emanating surface of stationary support 12. Upon application of pressurized fluid to the opening of the fluid collimating conduit 14 in fluid communication with a pressurized manifold containing pressurized fluid, the single fluid collimating conduit 14 produces an orthogonal jet emanating from the gas emanating surface. The velocity vector of the orthogonal jet, indicated by the arrows in FIG. 1a, is parallel to the dashed normal line 16 and is normal to a surface of moveable substrate 10 and to the surface of gas-emanating stationary support 12. The orthogonal jet thus impinges in an orthogonal fashion on the opposing surface of moveable substrate 10. When sufficient fluidic pressure is applied to produce an orthogonal jet of sufficient pressure and velocity, the moveable substrate 10 is fluidically levitated but is unstable with respect to lateral motion of the substrate.
FIG. 1b illustrates a different embodiment of the prior art and shows a cross-sectional view of the stationary support 12 containing the single fluid collimating conduit 14 that is in fluid communication with a pressurized manifold (not shown). Dashed lines 16 are normal to a surface of moveable substrate 10 and to the surface of stationary support 12. Upon application of pressurized fluid to the opening of the fluid collimating conduit 14 in fluid communication with a pressurized manifold containing pressurized fluid, the single fluid collimating conduit 14 produces a non-orthogonal jet emanating from the surface of the stationary support 12. The single fluid collimating conduit 14, produces a non-orthogonal jet or tilted jet whose velocity vector, indicated by the arrow in FIG. 1b, is not parallel to the dashed normal line 16 and thus is not orthogonal to the surface of moveable substrate 10 and is not orthogonal to the surface of stationary support 12. The non-orthogonal jet thus impinges in a non-orthogonal fashion on the opposing surface of moveable substrate 10. When sufficient fluidic pressure is applied to the fluid flowing through the fluid collimating conduit 14 to produce a non-orthogonal jet of sufficient pressure and velocity, the moveable substrate 10 is fluidically levitated but is unstable with respect to lateral motion of the substrate. As mentioned previously, annular nozzles of the type described in U.S. Pat. Nos. 5,492,566 and 5,967,578 are formed when the spacing between a plurality of tilted jets positioned around the circumference of a circle becomes infinitely small and the plurality of orifices or fluid collimating conduits 14 from whence the tilted jets emanate are arranged about the circumference of a circle in such a manner that projection of each tilted jet on the gas emanating surface is aligned parallel to a radius of said circle and the fluid flow of each tilted jet is directed away from the center of the circle.
FIG. 2 shows a cross-sectional view illustrating one embodiment of the prior art disclosed in U.S. Pat. No. 5,370,709 (discussed above) that is frequently employed to address the difficulty of positional instability during fluidic levitation using gasses. U.S. Pat. No. 5,370,709 discloses the stationary support 12 containing the single fluid collimating conduit 14 in fluid communication with a pressurized manifold (not shown). The single fluid collimating conduit 14 produces a single orthogonal jet whose velocity vector indicated by the arrows in FIG. 2 is parallel to the dashed normal line 16 normal to a surface of moveable substrate 10 and to a surface 24 of stationary support 12. The orthogonal jet thus impinges in an orthogonal fashion on the opposing surface of moveable substrate 10. Stationary support 12 also contains at least one protruding feature 26 extending above the surface 24 of stationary support 12 in the direction of moveable substrate 10 and is located on the surface 24 of stationary support 12 so as to impede horizontal lateral motion of moveable substrate 10 in the direction parallel to surface 24 of stationary support 12. FIG. 2 illustrates the use of physical stops, exemplified by protruding feature 26, that is commonly employed for the purposes of stabilizing the position of the moveable substrate 10 during fluidic levitation so that the moveable substrate 10 remains essentially centered over the single fluid collimating conduit 14 that supplies an orthogonal jet whose velocity vector is parallel to and essentially coincident with a normal to the surface 24 illustrated by the dashed normal line 16. The location of the fluid collimating conduit 14 in the gas-emanating surface is taken as an alignment feature and the moveable substrate 10 is positioned at a desired location relative to the alignment feature. The locations of the protruding features 26 can also be taken as alignment features for positioning of the moveable substrate 10 at a desired location before initiating the fluid flow required for pneumatic levitation.
Reactive Chemical Fluid Flow
The presence of reactive chemical substances in the fluid flow during fluidic levitation can cause complication with equipment operation. In this disclosure, the terms reactive chemical substance, chemically reactive reagent, reactive reagent, reactive chemical, reactive substance, and reactive material will all refer to composition of matter that is not chemically inert to at least one of the materials of construction of the fluid delivery system. In particular, the presence of reactive reagents in the orthogonal jet can cause complications with equipment operation. As taught in the art of fluidic levitation for substrate processing, reactive materials in the fluid flow can react with surfaces of the fluid delivery system and, more importantly, the orifice or orifices or the fluid collimating conduits 14 in the fluid emitting stationary support. The prior art of substrate processing using fluidic levitation methods is focused on primarily on high temperature processes operating above 500° C. An example of a high-temperature process that can be operated using fluidic levitation is chemical vapor deposition. The art teaches that one approach to controlling the chemical reactivity of the fluid flow is to control the temperature of the fluid. This approach is satisfactory if the fluid exhibit chemical reactivity is strongly temperature dependent; however, more recent developments in substrate processing utilize chemical substances in the process fluid flow that are highly reactive with fluid delivery system materials of construction even at room temperature. Highly reactive materials whose reactivity is appreciable even at room temperature are present in the fluid flows that are employed in, for example, atomic layer deposition processes. Some of the highly reactive materials in the low temperature fluid flows of atomic layer deposition processes are organometallic compounds, ozone, metal halides, metal amides, and other reactive fluid substances.
It is desirable, then, to be able to manage the chemical interactions of the highly reactive precursor reagents in the fluid employed for fluidic levitation. If the fluid delivery system surfaces are chemically reactive with the fluid flow then elements of the fluid delivery system whose critical dimensions must be maintained for robust system operation may change over time becoming larger, smaller, or even failing altogether. The chemical reactivity of the fluid delivery system must, therefore, be managed when non-chemically inert materials are employed as part of the fluid composition of matter in the fluid delivery system during fluidic levitation.
Spatially Ordered Fluid-Flow
U.S. Pat. No. 3,368,760 by C. C. Perry titled “Method and apparatus for providing multiple liquid jets” and U.S. Pat. No. 3,416,730 by C. C. Perry titled “Apparatus for providing multiple liquid jets” both describe methods and apparatus for producing compound liquid fluid flows and compound liquid jets. Both U.S. Pat. Nos. 3,368,760 and 3,416,730 disclose methods and apparatus for compound coaxial jet formation with viscous fluids like liquids, fluid aerosols, and non-gaseous liquid-like flowable substances including emulsions, dispersions, resins, colloids, suspensions, and composite. Additional fluid-like materials disclosed in U.S. Pat. No. 3,368,760 include gaseous particle suspensions such as those found when a gas is used to propel a powder through a discharge passage. U.S. Pat. Nos. 3,368,760 and 3,416,730 teach the use of pressure comparators to equalize the velocity of the inner primary liquid jet with the secondary liquid jet velocity in order to prevent mixing and turbulence during compound jet formation, teach the use of switchable valves to vary the overall composition of the compound jet, and teach the use of concentric fluid emitting nozzles for the purpose of formation of a coaxial compound jet with at least a primary fluid jet and a secondary fluid jet sheath in contact with and surrounding the primary fluid jet. In general, both U.S. Pat. Nos. 3,368,760 and 3,416,730 teach the use of a compound coaxial jet as method to transport a reactive primary fluid by employing a sheath of secondary fluid that is in contact with and surrounds the primary fluid as a means of modulating the reactivity of the primary fluid.
Another disclosure of the concept of compound jet is found in U.S. Pat. No. 4,196,437. U.S. Pat. No. 4,196,437 by C. H. Hertz titled “Method and apparatus for forming a compound liquid jet particularly suited for ink-jet printing” describes the use of compound liquid jet to form fine droplets for ink-jet printing applications. The apparatus described by Hertz employs a primary stream formed by ejecting under pressure a primary liquid from a nozzle and then causing the primary stream to traverse a thin layer of a secondary fluid to form a compound liquid stream which breaks up to form a compound jet of fine droplets each containing both the primary liquid and the secondary fluid. U.S. Pat. No. 4,196,437 teaches that the primary fluid, the secondary fluid, or both the primary and secondary fluid may be reactive fluids. More importantly, the secondary fluid is essentially a stationary fluid through which the primary fluid traverses, with the result that the secondary fluid is dragged along with the primary fluid jet by fluid momentum interactions. The method of formation of compound jets of the present invention does not employ stationary fluid reservoirs or layers, thereby distinguishing it from U.S. Pat. No. 4,196,437. Additionally, the use of compound jets for fluidic levitation is not mentioned or anticipated anywhere in U.S. Pat. No. 4,196,437.
The concept of a compound jet was further articulated in the open scientific literature by Hertz and Hermanrud in 1983 (J. Fluid Mech. (1983), vol 131, pp 271-287). Hertz and Hermanrud disclosed “a new type of liquid-in-air jet generated by a primary fluid jet that emerges from a nozzle below the surface of a stationary (secondary) fluid. After breaking the surface, the jet consists of the central primary jet surrounded by a sheath of secondary fluid which has been entrained by the primary jet during its passage through the secondary fluid.” Hertz and Hermanrud call this new type of jet a “compound jet” formed from a primary and a secondary fluid. According to Hertz and Hermanrud the compound jet is comprised of a central primary jet of primary fluid that is surrounded by a sheath of secondary fluid. The article also teaches that the flow in the compound jet is essentially laminar and that the primary and secondary fluids can only mix by diffusion. Mixing by diffusion is a relatively slow process thus the primary and secondary fluids in the compound jet remain compositionally segregated as the jet propagates though space.
U.S. Pat. No. 6,377,387 B1 discloses a method for preparing particles for use in electrophoretic displays and an apparatus for the formation of compound liquid jets as defined by Hertz and Hermanrud (loc cit) for the purpose of producing substantially uniformly-sized droplets of a first phase, the first phase including a fluid and particles, for introduction into a second phase, for producing substantially uniformly-sized complex droplets having a core formed form a first phase, the first phase including a fluid and particles, and a second phase that surrounds the first phase as a shell. There is no mention or anticipation of the use of compound jets for fluidic levitation processes in U.S. Pat. No. 6,377,387 B1.
WO 02/100558 A1 by Larrell and Nilsson titled “Device for Compound Dispensing” discloses a MEMS based apparatus for dispensing very small amounts of compound volumes of liquids. The apparatus employs a drop-on-demand type fluid ejector to produce a transient fluid jet for a primary fluid traversing a stationary fluid reservoir comprised of a secondary fluid to produce a transient compound liquid jet comprised of a primary fluid stream surrounded by a sheath of secondary fluid that produces an encapsulated drop upon breakoff. There is no mention or anticipation of the use of compound jets for fluidic levitation processes in WO 02/100558 A1.
U.S. Pat. No. 6,699,356 B2 by Bachrach and Chinn titled “Method and apparatus for chemical-mechanical jet etching of semiconductor structures” and U.S. Pat. No. 7,037,854 B2 by Bachrach and Chinn titled “Method for chemical-mechanical jet etching of semiconductor structures” disclose the use of at least one liquid jet impinging on a substrate for the purpose of carrying out various etching operations and processes on various semiconductor substrates. In an alternate embodiment U.S. Pat. Nos. 6,699,356 B2 and 7,037,854 B2 disclose the use of at least one gas jet impinging on a substrate for the purpose of carrying out various etching operations and processes on various semiconductor substrates. The fluidic jets impinge on the surface of a substrate mounted on a substrate holder, said fluidic jet impinging preferably in a non-orthogonal manner so as to minimize the stagnation area on the substrate surface at the jet impingement location. The dual nozzle jets are described in U.S. Pat. No. 7,037,854 B2 at col. 4, lines 30-37 and U.S. Pat. No. 6,699,356 B2 at col. 4, lines 21-28) “dual nozzle, or nozzle within a nozzle (see FIG. 2), in which a concentric annular outer orifice 201 surrounds a central orifice 203, and discharges a secondary high pressure flow of fluid 205, forming a spray curtain surrounding and containing the jet cone 207 for the central orifice, thereby creating a more narrowly focused jet.” Clearly, the jet described in U.S. Pat. Nos. 6,699,356 B2 and 7,037,854 B2 is not the same as previous art, but is rather a single jet surrounded by a spray curtain of droplets and the fluid discharges from the secondary high pressure fluid flow is not in intimate contact with the primary high pressure fluid flow from the central orifice. Unlike the prior art of compound jets as described in detail by Hertz and Hermanrud (loc cit), different jet trajectories for the secondary high pressure flow of fluid 205 from the annular outer orifice 201 and a primary high pressure jet cone 207 from the central orifice 203 are used. There is no mention or anticipation of the use of compound jets for fluidic levitation processes in U.S. Pat. Nos. 6,699,356 B2 and 7,037,854 B2.
U.S. Patent Application Publication No. 2012/0203315 A1 by Ripoll et al titled “Method for producing nanofibres of epoxy resin for composite laminates of aeronautical structures to improve their electromagnetic characteristics” describes method for improving the electrical properties of carbon composite materials by application of layers of carbon nanotubes dispersed in epoxy and applied to the carbon composite structure by deposition of nanofibers produced by electrospinning. A compound liquid coaxial jet as defined by Hertz and Hermanrud (loc cit) is produced during the electrospinning process where the primary fluid comprising the interior jet is doped with a sufficient amount of carbon nanotubes or other conductive particles or conductive nanoparticles exceeding the percolation threshold for electrical conductivity and the secondary fluid providing a surrounding sheath for the primary fluid is an epoxy resin dissolved in a solvent. During electrospinning, the field induced Taylor cone formation followed by compound nanojet formation and solvent loss results in the formation of conductive nanofibers deposited on a carbon composite substrate according to the electric field patterns in the deposition system. U.S. Pat. No. 7,794,634 B2 by Ripoll et al titled “Procedure to generate nanotubes and compound nanofibres from coaxial jets” further elaborates on the application of coaxial compound liquid jet for the formation of materials using electrospinning methods. U.S. Pat. No. 7,794,634 B2 teaches a compound fluid jet wherein the primary fluid is a liquid and the secondary fluid providing a surrounding sheath for the primary fluid is a fluid that solidifies before the compound jet breaks up into drops. The compound jet is U.S. Pat. No. 7,794,634 B2 is formed by means of electrospinning whence the field induced Taylor cone formation followed by compound nanojet formation and secondary fluid solidification results in the formation of tubular nanofibers when the primary fluid is removed. Additionally, the formation of compound nanotubes is taught when both the primary and secondary fluids solidify before jet breakup the electrospinning. Further detail on applications of compound jets to the formation of capsules and particles for food products is given in U.S. Pat. RE44,508 E by Ripoll, Calvo, Loscertales, Bon, and Marquez titled “Production of capsules and Particles for improvement of food products”. U.S. Pat. RE44,508 E teaches the use of a coaxial compound jet with a primary fluid surrounded by a sheath of secondary fluid generated by electrohydrodynamic forces to produce encapsulated particles upon jet breakup. The coaxial jet must have at least one conducting fluid for the electrohydrodynamic jet to form and either the conducting fluid may be the primary fluid or the secondary fluid. Alternatively, both the primary and secondary fluids may be conducting and contribute to the formation of the electrified jet during an electrospinning-like process. The secondary fluid is used to encapsulate the primary fluid during both jet formation and drop formation during jet breakup. U.S. Pat. RE44,508 E teaches the use of biocompatible fluids in the coaxial compound jet in an electrospray process to produce biocompatible encapsulated particles as vehicles for additives in food formulation. There is no mention or anticipation of the use of compound jets for fluidic levitation processes in U.S. Patent Application Publication No. 2012/0203315 A1, U.S. Pat. No. 7,794,634 B2, or U.S. Pat. RE44,508 E.
U.S. Pat. No. 8,361,413 B2 by Mott et al titled “Sheath flow device” discloses an apparatus providing a means of forming compound jets where a primary fluid flow is in contact with and surrounded by a secondary fluid flow. The device is comprised of a sheath flow system having a channel with at least one fluid transporting structure located in the top and bottom surfaces situated so as to transport the sheath fluid laterally across the channel to provide sheath fluid fully surrounding the core solution. Although U.S. Pat. No. 8,361,413 B2 does not disclose the use of the sheath flow device for the formation of coaxial or collinear compound jets, the apparatus described provides a means for producing compound fluid flows that are useful for compound jet formation and may be used to produce compound jets by, for example, electrohydrodynamic jet formation or other means with suitable fluid formulations.
U.S. Patent Application Publication No. 2014/0027952 A1 by Fan et al titled “Methods for producing coaxial structure using a microfluidic jet” and U.S. Patent Application Publication No. 2014/0035975 A1 by Eissen et al titled “Methods and apparatuses for direct deposition of features on a surface using a two component microfluidic jet” disclose the use of compound microfluidic jets for writing patterns on surfaces and for other applications. Both U.S. Patent Application Publication Nos. 2014/0027952 A1 and 2014/0035975 A1 describe a method for producing coaxial compound jets where a primary liquid is surrounded and in contact with a sheath of a secondary liquid. The surrounding secondary sheath liquid may be chemically inert, chemically reactive with itself in some manner like a UV curable monomer, or chemically reactive with the primary liquid in some manner. Methods are described for generating multi-component flow for the purposes of producing micro-fluidic jets that are used in printing processes. Both U.S. Patent Application Publication Nos. 2014/0027952 A1 and 2014/0035975 A1 describe methods and apparatus for hydrodynamic focusing of coaxial liquids jets to control the diameter of the primary fluid jet as well as methods for producing compound coaxial liquid jets that are undisturbed by Rayleigh breakup for extended periods of time so that the compound coaxial jet itself may be employed as a means of mass transport during printing and deposition processes. There is no mention or anticipation of the use of compound jets for fluidic levitation processes in either U.S. Patent Application Publication 2014/0027952 A1 or 2014/0035975 A1.
Compound Fluid Flows
Compound fluid flows are a type of spatially and compositionally ordered fluid flows. Fluidic levitation of a moveable substrate using an orthogonal jet emanating from a stationary support requires a fluid. The fluid may be either compressible or non-compressible. An example of a compressible fluid is a gas like air, argon, or nitrogen and an example of a non-compressible fluid is a liquid like water or a hydrocarbon fluid. The fluid can have a naturally mixed composition, as in the case of air, or the fluid can have an intentionally varied composition. Intentionally varied fluid compositions are particularly useful for some applications of both hydraulic and pneumatic levitation. The use of intentionally varied fluid compositions requires a means of generating varied fluid compositions.
An unconfined stream of rapidly moving fluid is called a jet. A jet may be formed from either incompressible fluids, such as water, or compressible fluids such as gasses. A jet of fluid whose cross-section does not have a uniform chemical composition is called a compound jet. Compound jets can be formed with either compressible or non-compressible fluids. Compound jets can be formed by several means such as those described by Hertz in U.S. Pat. No. 4,196,437 for non-compressible fluids such as liquids. Formation of gaseous compound jets is known to those skilled in the art of aeronautics and gaseous fluid compound jets are employed in the study and development of turbine engines for aeronautic applications. The production of gaseous fluid compound jets is accomplished by several methods, mostly commonly through the formation of coaxial compound jets or collinear compound jets.
Fluid movement is described by the fluid velocity vector that contains the information about the spatial direction of fluid movement relative to some reference direction and whose scalar magnitude describes the velocity of the fluid movement. The fluid flow axis is defined by line parallel to and superimposed upon the direction of the velocity vector of the jet taken at the centroid of the cross-section of the jet. Put another way, the fluid-flow axis is defined by a line passing through the centroid of the cross-section of the fluid flow that is parallel to and superimposed upon the direction of the velocity vector at the centroid of the cross-section of the fluid flow. The fluid flow axis describes the movement of the fluid comprising the flow at the centroid of the cross-section of the fluid flow. The fluid flow may be a jet of fluid.
Definition of a collinear compound fluid flow: A collinear compound fluid flow is a compound fluid flow in which fluids of at least two different chemical compositions are present and the chemical composition of the fluid varies within the cross-section of the fluid flow such that regions of similar chemical composition flow in parallel paths that are collinear with the fluid flow axis defined by the direction of fluid propagation at the centroid of the cross-section of the fluid flow. The fluid flow may be a jet.
Definition of a coaxial compound fluid flow: A coaxial compound fluid flow is a compound fluid flow in which fluids of at least two different compositions are present and the chemical composition of the fluid flow varies across the cross-sectional area of the fluid flow such that regions of similar chemical composition are segregated into annuli or into circular regions, each region being centered around the same fluid flow axis defined by the velocity vector of the fluid flow taken at the center of the cross-section of the fluid flow so that one region of chemical composition is entirely surrounded by a region of different chemical composition as the regions flow collinearly and simultaneously along an axial direction. The fluid flow may be a jet.
A compound coaxial fluid flow is also a special type of compound collinear fluid flow that has a specific annular arrangement of different chemical compositions. A compound collinear fluid flow may also possess at least one characteristic of a coaxial fluid flow such that one region of chemical composition may be entirely surrounded by a region of different chemical composition as the regions flow collinearly and simultaneously along an axial direction. A difference between a collinear and a coaxial fluid flow is that a collinear jet is not necessarily completely symmetric about the fluid flow axis whilst the coaxial jet is always symmetric about the fluid flow axis.
Thus, a compound fluid flow may have both collinear and coaxial characteristics as defined by the arrangement of regions of different chemical composition within the fluid flow relative to the fluid flow axis as defined by the direction of fluid flow propagation. The chemical distribution in a compound fluid flow changes as a function of time because of lateral diffusion of chemical species. The degree of lateral diffusion which results in a redistribution of chemical concentrations in the cross-section of the fluid flow depends several factors including temperature, fluid velocities, and fluid viscosities. In condensed phases and incompressible fluids the lateral diffusion is small. In compressible fluids near or above atmospheric pressure the lateral diffusion between regions of differing composition is small. If the distance that the compound fluid travels is small relative to the fluid velocity, then the composition and chemical distribution in the compound fluid flow remains essentially unchanged during the transit time of the fluid flow. This is desirable from a process standpoint as it now provides a means for encapsulating reactive precursors with an inert fluid so they can be transported to the moveable substrate surface during the fluidic levitation process.
Atomic Layer Deposition
Atomic layer deposition is a method of forming layers on a substrate that have a well-controlled atomic structure. Such layers can be a single atom thick. Conventionally, the layers are formed by providing a substrate in a vacuum chamber and reacting a first gas with the substrate surface to deposit a single layer of atoms or molecules on the substrate. The first gas is then purged, typically with an inert gas such as nitrogen, and a second gas is reacted with the layer and then purged. By alternately providing gases and purging them, atomic layers of material are built up on the substrate.
Because the atomic layers are so thin, many reaction-purge cycles are necessary to form a thick structure. In consequence, it is preferred to perform each cycle of the operation very quickly, for example within milliseconds. However, the provision and removal of gases in a vacuum typically requires pumping the gases into and out of the vacuum chamber. This process can take seconds, or even minutes. There is therefore a need for rapidly providing gases over a substrate surface.
A prior-art method of forming thin films on a substrate using fluid-flow levitation for atomic-layer deposition is taught in US Patent Application Publication No. US 2009/0130858 A1, published by Levy, on May 21, 2009. This approach uses a gas bearing to support a substrate on a head providing spatially alternate flows of inert and reactant gases. The rate at which layers of material are deposited on the substrate depends on the number of alternating gas flows, and hence the head size, and the rate at which the substrate passes over the head.
There is a need, therefore, for an improved apparatus and method for forming thin films on a substrate using atomic layer deposition that is compatible with existing equipment, provides fast and uniform dispersion of a gas over a substrate in a chamber, and prevents unwanted reactions on chamber surfaces.